The present invention relates generally to the optimization of designs of castings for manufacturing and, more particularly, to systems and methods for quickly and reliably evaluating manufacturability of casting designs.
Due to low manufacturing costs, high flexibility, and near net shape forming, castings increasingly are being used in a large number of industries. In many industries, castings are designed mechanically to meet desired functional requirements. As such, little consideration is given to the manufacturability of the castings not only because there exists a general lack of understanding of the significance of designing castings for manufacturing, but also because computational systems and tools generally are unavailable for casting designers to access to easily and reliably evaluate the manufacturability of the castings, not to mention the limited capabilities of currently available computational systems and tools. As used herein, “conventional” refers to technologies, such as, but not limited to practices, methods, systems, and tools, of the prior art, i.e., that were in existence and publicly disclosed prior to the conception of the present invention.
For example, in conventional casting design practices, casting designers forward casting designs to casting analysts and/or machining analysts for cast-ability and machine-ability evaluations. This remains the practice even though common manufacturability evaluations are very limited in their evaluating abilities. For instance, in cast-ability evaluations, interpretation of computed results heavily relies on the expertise of casting analysts. In addition, even with availability of sophisticated casting process simulation modules and user interfaces that provide colorful visualization of predicted results of heat transfer and fluid flow events that occur during casting processes, it remains difficult and time consuming to systematically optimize casting designs without demanding significant human interaction and numerous manual trial-and-error interactions. As a result, conventional casting design processes generally entail lengthy development cycles and low reliability for determining manufacturability due to variations in individual knowledge and experience of those evaluating the casting designs and the manufacturability thereof.
In addition, a fundamental problem facing foundries is the development of an adequate riser design for feeding a casting. The conventional approach to riser size estimation is to calculate the volume and cooling surface area of various parts or areas of the casting and use those measurements to derive the geometric modulus. Areas of the casting that have the lowest geometric modulus values solidify first, while those regions with the highest geometric modulus values solidify last. In general, the geometric modulus values govern the design of the riser in heavy-section castings. While these concepts may be simple and straightforward, their implementation in casting design is not. This is due to the difficulty in manually calculating volumes and surface areas for complex castings. In industry applications, the approach taken by most foundry engineers is similar to that of weight calculation. The casting design is arbitrarily broken into a number of pieces, and each of these pieces is identified as a simple geometric shape for which surface area and volume can be calculated. In practice, however, this process is cumbersome and inaccurate. The arbitrariness of approximating a casting design with a series of simple shapes reduces both repeatability and accuracy. Another intrinsic problem with this method is that it is based only on geometry as it does not directly take into account thermal effects, such as specific properties of chilling or insulating materials and heat saturation of cores or various areas of the mold. While some factors have been proposed to correct these effects, such factors can increase the uncertainty surrounding the accuracy of results.
More recently, use of computer simulations of casting-related manufacturing processes using three-dimensional computer models has become increasingly widespread. Such simulations can predict, to a certain degree of accuracy, the progressive solidification of the casting and its rigging system and the potential for casting defect formation. One drawback of the use of such simulations, however, is that it requires an initial casting design to evaluate in simulated processes. Many foundries, even those using the most advanced simulation tools, still use a conventional approach when developing the initial casting design for simulation. In general, this requires calculating approximate surface areas, volumes, and geometric modulus values through manual or software-based methods to break the casting design into simple shapes.
Additionally, because of metal and alloy shrinkage and, in particular, thermal non-uniformity during cooling in solidification process and quench process of heat treatment, the final cast components can have high residual stress levels and significant geometric distortion prior to machining. It is generally believed that residual stress levels in castings are related primarily to the geometric design of the casting, especially during the heat treatment process. More particularly, high stress levels developed in the casting can lead to hot tear during solidification and cracking or severe distortion of the casting during heat treatment process. Unfortunately, there is no simple and reliable method, tool, or system available for easily and quickly checking a manufacturability of a casting. In evaluating machining feasibility of a casting, for example, the machining analyst requires final geometrical information of the casting after solidification and/or heat treatment depending upon the manufacturing process defined. The precise predictions or measurements of the final geometric dimensions of the casting are very important for accurate evaluation of an ability of a casting to be machined during a machining process. Actual measurement of the final casting components is doable, but expensive and time-consuming.
As such, there exists a need for a system for easily and reliably evaluating manufacturability of casting designs. In particular, there is a need in the art for systems and methodologies that allow casting designers to quickly assess the manufacturability of casting designs proposed for manufacturing and, further, to optimize casting designs for manufacturability including, but not limited to, geometric design-ability, cast-ability, heat treat-ability, and machine-ability.